1. Field of the Invention
The present invention generally relates to oncological radiation therapy and more particularly to use of motion compensated treatment plans.
2. Background Description
Radiation therapy for cancerous tumors may involve adverse side effects because of the difficulty of confining the radiation to the target tumor. Side effects may range from temporary damage to healthy tissues that regenerate following treatment to irreversible damage to healthy tissues that cannot regenerate. Side effects of radiation can be minimized by planning and delivery of a course of radiotherapy. For example, where treatment technology involves irradiation of healthy tissue in addition to the tumor, a treatment plan may use a succession of doses that allows time between successive doses for damaged tissues to regenerate, and where each dose is small enough to avoid damage to tissues that cannot regenerate. Typically, a treating physician will use a dose volume histogram (DVH) to prescribe radiation therapy and a radiation technician will apply a delivery technology so as to conform to the prescribed DVH as closely as possible. Various techniques have been developed to enable a prescribed DVH to be followed more closely and with reduced side effects.
One such technique is conformal radiotherapy (CRT), which has been in use since 1960. This uses a single radiation beam, with special blocks or collimators to more tightly control the treatment field. Since the late 1990's a more versatile approach to conformal radiotherapy has been in use. This approach uses radiation beams made up of hundreds of small components, allowing the treatment field to follow curves and contours of the tumor. This approach is called Intensity Modulated Radiation Therapy (IMRT), and typically requires very detailed treatment planning along with computer analysis.
Another group of techniques has been developed to compensate for motion of tumors in the patient during treatment (e.g. where doses of radiation must be administered to a thoracic tumor which moves as the patient breathes). Four Dimensional Computed Tomography (4D CT) scanning techniques are used to adjust the delivered radiation field to compensate for tumor motion over the breathing cycle.
Commercial algorithms exist for intensity modulated radiotherapy delivery, and for using four dimensional computed tomography scans. However, no feasible treatment planning algorithm exists for using IMRT on 4D CT scans, with the intensity modulated radiation field being provided by a linear accelerator (linac) and a dynamic multi-leaf collimator (DMLC).